This invention relates in general to coking and in particular to a new and useful process for cooling crude coke oven gas.
This invention concerns a process for cooling the crude coke oven gas drawn from a gas collecting main down to a gas temperature of less than 20.degree. C. after separating the collecting main flushing liquid fed to a tar separator.
The crude coke oven gases produced in the coking of coal in coking furnaces comprise primarily uncondensable coke oven gas, H.sub.2, CH.sub.4, etc., and condensable and absorbable fractions such as tar, crude benzene, water, ammonia, hydrogen sulfide, carbon dioxide, and hydrogen cyanide.
In the cooling of the hot gases at a temperature of 800.degree. to 900.degree. C. by a water spray in the gas collecting main down to 80.degree. to 82.degree. C., a major fraction of the tar constituents is condensed out, while the lower-boiling fraction of the tar is fed with the gas and the other components to the indirect or direct gas precoolers for further cooling, as a rule to 20.degree. to 30.degree. C. When leaving the collecting main, the crude gas is saturated with steam. During the further cooling of the gas in the coolers, the water fraction and other tar constituents condense. One component of the tar is naphthalene, which can then sublime directly out of the vaporphase during the further cooling of the crude gas into the solid phase, when there is no longer equilibrium between the condensed components, i.e., when the dissolving power of the condensed components, i.e., when the dissolving power of the condensed tar and of the water for naphthalene is exceeded. In such a case, naphthalene is deposited on the cooling surfaces of the precooler.
A process is know from German patent application Disclosure No. 26 52 499 for the treatment of coking plant gas in an indirect precooler after separating the collecting main flushing liquid fed to a tar separator, in which the precooler is divided into two stages and the condensate forming in the precooler is fed to a tar sink from which a liquid is withdrawn that is enriched with tar, with which the gas is sprayed between the two stages, with the spraying of the gas taking place before its temperature has dropped below the temperature at which naphthalene is deposited from the gas.
Unfortunately, practical experience shows that this process is unsuitable for cooling the coke plant gas to a sufficiently low level. Since no additional flushing tar is used, the temperature limit is determined by the formation capability of the tar condensed out in the cooler. It has been found that the naphthalene saturation limit of the tar-naphthalene mixture, forming after the precooler, is exceeded even at a crude gas temperature of 25.degree. C., and the familiar plugging occurs in the lower area of the precooler. In practice, the first plugging occurs even at approx. 28.degree. C.
On the other hand, it is a problem to supply the condensate forming directly to the separator, since emulsions can form there.